The invention relates to communication devices and, in particular, to communication devices being able to read-out and, possibly, store voice messages in a memory. The invention also relates to methods for retrieving and, possibly, storing voice messages in such devices.
A communication device adapted to receiving and transmitting audio signals is often equipped with a speech encoder and a speech decoder. The purpose of the encoder is to compress an audio signal which has been picked-up by a microphone. The speech encoder provides a signal in accordance with a speech encoding format. By compressing the audio signal the bandwidth of the signal is reduced and, consequently, the bandwidth requirement of a transmission channel for transmitting the signal is also reduced. The speech decoder performs substantially the inverse function of the speech encoder. A received signal, coded in the speech encoding format, is passed through the speech decoder and an audio signal, which is later outputted by a loudspeaker, is thereby recreated.
One known form of a communication device being able to read-out and store voice messages in a memory is discussed in the U.S. Pat. No. 5,499,286 by Kobayashi. A voice message is stored in the memory as data coded in the speech encoding format. The speech decoder of the communication device is used to decode the stored data and thereby recreating an audio signal of the stored voice message. Likewise, the speech encoder is used to encode a voice message, picked up by the microphone, and thereby providing data coded in the speech encoding format. This data is then stored in the memory as a representation of the voice message.
The U.S. Pat. No. 5,630,205 by Ekelund illustrates a similar design.
Whilst the known communication device described above functions quite adequately, it does have a number of disadvantages.
A drawback of the known communication device is that although the speech encoder and speech decoder allow message data to be stored in a memory in a relatively compressed format, a large memory is still needed. Memory is expensive and is often, especially in small hand-held communication devices, such as cellular phones or mobile phones, a scarce resource.
An example of a speech encoding/decoding algorithm is defined in the GSM (Global System for Mobile communications) standard where a residual pulse excited long term prediction, RPE-LTP coding algorithm is used. This algorithm, which is referred to as a full-rate speech coder algorithm, provides a compressed data rate of about 13 kbit/s. The memory requirement for storing voice messages is thereby relatively high. The computational power needed for performing the full-rate speech coding algorithm is, however, relatively low (about 2 MIPS). The GSM standard also includes a half-rate speech coder algorithm which provides a compressed data rate of about 5.6 kbit/s. Although this means that the memory requirement for storing voice messages is lower than what is required when the full-rate speech coding algorithm is used, the half-rate speech code algorithm does require a lot of computational power (about 16 MIPS). Computational power is expensive to implement and is often, especially in small hand-held communication devices, such as cellular phones or mobile phones, a scarce resource. Furthermore, a circuit for carrying out a high degree of computational power also consumes a lot of electrical power, which adversely affect the battery life-length in battery powered communication devices.
It is an object of the present invention to provide a communication device which overcomes or alleviates the above mentioned problems.
The invention is also directed to a method by which the described device operates.
According to an aspect of the present invention there is provided a communication device comprising a microphone for receiving an acoustic voice signal thereby generating a voice signal, a speech encoder adapted to encoding the voice signal according to a speech encoding algorithm, the voice signal thereby being coded in a speech encoding format, a transmitter for transmitting the encoded voice signal, a receiver for receiving a transmitted encoded voice signal, the received encoded voice signal being coded in the speech encoding format, a speech decoder for decoding the received encoded voice signal according to a speech decoding algorithm, a loudspeaker for outputting the decoded voice signal, a memory for holding message data corresponding to at least one stored voice message, memory read out means for reading out message data corresponding to a voice message from the memory and code decompression means for decompressing read out message data from a message data format to the speech encoding format.
According to another aspect of the present invention there is provided a voice message retrieval method comprising the steps of reading out message data coded in a message data format from the memory, decompressing the read out message data to the speech encoding format by means of a decompression algorithm, decoding the decompressed message data according to the speech decoding algorithm, and passing the decoded message data to the loudspeaker for outputting the voice message as an acoustic voice signal.
According to another aspect of the present invention there is provided a voice message retrieval method comprising the steps of reading out message data coded in a message data format from the memory, decompressing the read out message data to the speech encoding format by means of a decompression algorithm and passing the decompressed message data to the transmitter for transmitting the voice message from the communication device.
This construction and methods achieve the advantage that a voice message is stored in the memory in a more compressed format than the format provided by a speech encoder. Such a stored voice message is decompressed by the decompression means thereby recreating an encoded voice signal coded in the speech encoding format, i.e. the format provided after a voice signal has passed a speech encoder.
Preferably the communication device further comprises code compression means for compressing an encoded voice signal coded in the speech encoding format thereby generating message data coded in the message data format and memory write means for storing the compressed message data in the memory as a stored voice message.
According to another aspect of the present invention there is provided a voice message storage method comprising the steps of converting an acoustic voice signal to a voice signal by means of a microphone, encoding the voice signal by means of the speech encoding algorithm thereby generating an encoded voice signal coded in the speech encoding format, compressing the encoded voice signal according to a compression algorithm thereby generating message data coded in the message data format and storing the compressed message data in the memory as a stored voice message.
According to another aspect of the present invention there is provided a voice message storage method comprising the steps of receiving a transmitted encoded voice signal coded in the speech encoding format, compressing the received encoded voice signal according to a compression algorithm thereby generating message data coded in the message data format and storing the compressed message data in the memory as a stored voice message.
This construction and methods achieve the advantage that a user can store a voice message in the memory in a more compressed format compared to the speech encoding format.
Since a voice message is stored in the memory in a more compressed format than the format provided by a speech encoder, as is the case in the prior art, less memory is required to store a particular voice message. A smaller memory can therefore be used. Alternatively, a longer voice message can be stored in a particular memory. Consequently the communication device of the present invention requires less memory and, hence, is cheaper to implement. In, for example, small hand-held communication devices, where memory is a scarce resource, the smaller amount of memory required provides obvious advantages. Furthermore, a small amount of computational power is required due to the fact that simple decompression algorithms can be used by the decompression means.